Ultrasonic probes are widely used for medical diagnostic and treatment purposes. Recently, sector scan probes have become prominent. A typical sector scan probe is illustrated in U.S. Pat. No. 4,151,834, which shows a housing containing a DC servomotor that drives a mechanism for oscillating a transducer crystal. Periodically, the transducer pulsed with electrical signals causing an ultrasonic beam to be emitted periodically as the transducer oscillates between its angular limits. The rate at which the transducer is pulsed is many times greater than the rate of angular movement of the transducer; and for this reason, the beam is said to scan a sector. Tissue interfaces in the path of each beam reflect energy back to the transducer, and the electronic circuitry associated with the probe establishes the distance of the interface from the transducer in a conventional manner. Medically useful information is made available when the output of the probe is displayed on a cathode ray tube (CRT). That is to say, the CRT displays the sector swept out by the beam as the transducer oscillates, and the circuitry that responds to echoes modulates the image on the CRT for presenting a sectoral cross-section through a patient being imaged.
In order to correctly display images on the CRT, the angular position of the transducer must be accurately known; and, to this end, it is conventional to incorporate a position sensor into the probe for sensing the angular position of the transducer and to establish the azimuthal angle of the display in the CRT. The probe utilizes a servo-feedback circuit to control the position of the transducer, and the angular information thus determined is made available to the CRT for display purposes.
Some medical procedures are facilitated when a biopsy needle is used in conjunction with the ultrasonic probe, and for this reason special ultrasonic probes have been developed for this purpose. U.S. Pat. No. 4,108,165 is typical of conventional ultrasonic probes designed to facilitate the use of a biopsy needle. The U.S. Pat. No. 4,108,165 discloses an ultrasonic probe having an annular transducer periodically driven by an electronic circuit for producing ultrasonic beams that can be directed into the body of a patient under examination. No scanning of the beam is provided, however, and the transducer is mounted in a cylindrical housing having an axial bore concentric with the annular transducer. The housing contains a radial slit which extends the length of the housing, and which permits entry of a semi-circular tube attached to a stainless steel cap having a flange for receiving the opposite end of the housing opposite that contains the transducer.
The cap is also slotted so that after the cap and the tube are inserted into the probe, rotation of the cap will misalign the slot therein with the slotted housing, thereby defining a central circular opening into which a biopsy needle can be inserted for concentrically locating the biopsy needle within the probe. Spring loaded detents in the housing are engagable in a corresponding groove in the inner flange of the cap for the purpose of releasable holding the cap to the probe.
The arrangement in the U.S. Pat. No. 4,108,165 is suitable for many applications, but the complexity of the design, particularly the use of spring loaded detents and the complexity in manufacturing the stainless steel cap in terms of machining, result in a biopsy attachment which is complex and more expensive than necessary. In addition, the probe is not well adapted for use with a sector scan type of ultrasonic probe.
It is, therefore, an object of the present invention to provide a new and improved biopsy attachment for an ultrasonic probe which overcomes the above-described deficiencies in the prior art.